PM pans ALP prevarication on gay marriage

The Turnbull government is refusing to reveal whether it has a Plan B if the Labor caucus opts to formalise its opposition to a plebiscite on legalising same-sex marriage.

Instead, Malcolm Turnbull has lashed out at Opposition Leader Bill Shorten for "playing politics" rather than coming to a quick decision on where Labor stands.

"It just shows how political he is, how little he cares about same-sex couples, how little he cares about the right of same-sex couples to be married," the prime minister told reporters in Canberra on Monday.

The government had done everything it could to win the support of the crossbenchers, Labor and the Greens, Mr Turnbull says.

The Labor caucus meets on Tuesday to formally decide its position.

But Mr Shorten continues to insist the best way to achieve marriage equality is a free vote in parliament.

He and Labor frontbenchers have spoken to experts, same-sex couples and their families over the past few weeks and he says the level of community opposition to the plebiscite is extraordinary.

"Australia has never held a national opinion poll to judge anyone else's relationship, so people are legitimately asking why this should be inflicted on LGBTI Australians and their families."

Deputy Prime Minister Barnaby Joyce said Labor's likely opposition was "basically jettisoning any capacity for there to be a change in legislation".

Liberal Democrat senator David Leyonhjelm believes Labor would be making a serious mistake to oppose the plan.

Even if the plebiscite does happen on February 11 and is successful, Mr Turnbull faces dissent from conservatives in his party.

Veteran MP Kevin Andrews, who is strongly opposed to same-sex marriage, said he'll be looking at the national vote, the result in his electorate of Menzies, and whether the final bill contains what he deems adequate protections of freedom of speech and religion.

But he denied that meant he was claiming the right to a conscience vote.

"I'm not going to stand here and say that I'm going to vote one way or the other when there are a whole lot of hypotheticals at this stage to answer," he told reporters.